how to get dropdown id which is inside repeater Control

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Javascript

HTML

Dear Friends

I am having problem in getting dropdownlist Id which is in Repeater Control in Javascript..

i have tried it but it is not working

<script type="text/javascript">

      function ShowDDl() {

         var id = document.getElementById("<%= ChangeQuantityDDL.ClientID %>")

      }

  </script>

it gives me an Error that ChangeQuantityDDL do not exist in current context

<asp:Repeater ID="ItemListDL" runat="server"    >
<ItemTemplate>
                   <tr>
                       <td>
   <asp:Label ID="Label2" runat="server" Text='<%#Eval("Quantity")%>'></asp:Label><a href="#"  önclick="javascript:ShowDDl();"> Change</a><asp:DropDownList ID="ChangeQuantityDDL" runat="server" Visible="false">
                                <asp:ListItem>1</asp:ListItem>
                          <asp:ListItem>2</asp:ListItem>
                          <asp:ListItem>3</asp:ListItem>
                          <asp:ListItem>4</asp:ListItem>
                          <asp:ListItem>5</asp:ListItem>
                          <asp:ListItem>6</asp:ListItem>
                          <asp:ListItem>7</asp:ListItem>
                          <asp:ListItem>8</asp:ListItem>
                          <asp:ListItem>9</asp:ListItem>
                          <asp:ListItem>10</asp:ListItem>
                          <asp:ListItem>11</asp:ListItem>
                          <asp:ListItem>12</asp:ListItem>
                          <asp:ListItem>13</asp:ListItem>
                          <asp:ListItem>14</asp:ListItem>
                          <asp:ListItem>15</asp:ListItem>
                                                                                                                                  </asp:DropDownList></td>
                        <td>

please give me soluton for this as soon as possible..

Thanks in Advance..